Sorted By Test Name - Mayo Medical Laboratories

GALTK
84367
(galactose and galactose-1-phosphate) and/or determining the activity of the GALT enzyme, varies from
state to state. The diagnosis of galactosemia is established by follow-up quantitative measurement of
GALT enzyme activity. If enzyme levels are indicative of carrier or affected status, molecular testing for
common GALT mutations may be performed. If 1 or both disease-causing mutations are not detected by
targeted mutation analysis and biochemical testing has confirmed the diagnosis of galactosemia,
sequencing of the GALT gene is available to identify private mutations. The GALT gene maps to 9p13.
Several disease-causing mutations are common in patients with classic galactosemia (G/G genotype). The
most frequently observed is the Q188R classic mutation. This mutation accounts for 60% to 70% of
classical galactosemia alleles. The S135L mutation is the most frequently observed mutation in African
Americans and accounts for approximately 50% of the mutant alleles in this population. The K285N
mutation is common in those of eastern European descent and accounts for 25% to 40% of the alleles in
this population. The L195P mutation is observed in 5% to 7% of classical galactosemia. The Duarte
mutation (N314D) is observed in 5% of the general United States population. The above mutations, in
addition to the LA variant, are included in GAL6/84366 Galactosemia Gene Analysis (6-Mutation Panel)
and in GCT/84360 Galactosemia Reflex, Blood. See Galactosemia Testing Algorithm in Special
Instructions for additional information. Refer to Galactosemia: Current Testing Strategy and Aids for Test
Selection, Mayo Medical Laboratories Communique 2005 May;30(5) for more information regarding
diagnostic strategy.
Useful For: Second-tier test for confirming a diagnosis of galactosemia (indicated by enzymatic testing
or newborn screening) Carrier testing family members of an affected individual of known genotype (has
mutations included in the panel) Resolution of Duarte variant and LA variant genotypes
Interpretation: An interpretative report will be provided. Results should be interpreted in the context
of biochemical results.
Reference Values:
An interpretive report will be provided.
Clinical References: 1. Elsas LJ 2nd, Lai K: The molecular biology of galactosemia. Genet Med
1998 Nov-Dec;1(1):40-48 2. Kaye CI, Committee on Genetics, Accurso F, et al: Newborn screening fact
sheets. Pediatrics 2006 Sep;118(3):e934-963 3. Novelli G, Reichardt JK: Molecular basis of disorders of
human galactose metabolism: past, present, and future. Mol Genet Metab 2000 Sep-Oct;71(1-2):62-65
Galactosemia Gene Analysis, Known Mutation
Clinical Information: Classic galactosemia is an autosomal recessive disorder of galactose
metabolism caused by mutations in the galactose-1-phosphate uridyltransferase (GALT) gene. The
complete or near complete deficiency of the GALT enzyme is life threatening. If left untreated,
complications include liver failure, sepsis, mental retardation, and death. Galactosemia is treated by a
galactose-free diet, which allows for rapid recovery from the acute symptoms and a generally good
prognosis. Despite adequate treatment from an early age, children with galactosemia remain at increased
risk for developmental delays, speech problems, and abnormalities of motor function. Females with
galactosemia are at increased risk for premature ovarian failure. The prevalence of classic galactosemia is
approximately 1 in 30,000. Duarte variant galactosemia (compound heterozygosity for the Duarte variant,
N314D, and a classic mutation) is generally associated with higher levels of GALT activity (5%-20%)
than classic galactosemia (